Various systems are known for assisting the driver of a motor vehicle in carrying out automated recognition of road signs. Such recognition may be accomplished by using suitable devices for perceiving or detecting the surroundings. Such systems are available commercially both by various original equipment manufacturers (OEMs), typically in Europe, and by manufacturers of portable navigation devices (PNDs). The PND systems are based on GPS signals and, in some embodiments, on Galileo signals, in conjunction with map data for supplying the driver with information relating to road signs. A number of systems already use a camera device for improving the recognition accuracy and robustness. The manufacturers of vehicles use front-mounted camera devices and means for combining signals with data relating to the driving state of the vehicle. A further option is means for combining signals with navigation devices.
The above approaches have various disadvantages. As an example, it is not possible to recognize all road signs with accuracy. In these cases, a good recognition rate may be implemented for speed limit road signs and road signs prohibiting overtaking. However, road signs which are not consistent with traffic regulations, where such regulations exist (e.g., in Germany with the Viennese Road Traffic Convention), road signs are not recognized or are recognized with only a limited recognition rate. With respect to speed information, speed limits which are implicitly contained cannot be recognized by means of an optical device. Furthermore, situations also occur in which the surroundings cannot easily be assessed without the aid of the human eye. For example, when a plurality of road signs or contradictory road signs are present, and when road signs are missing it is not possible for satisfactory recognition or analysis to take place. In addition, GPS-based or Galileo-based information may be subject to a decreasing recognition rate over time. There is frequently also a need to avoid the combination of two or more recognition devices, with the use of a single device for recognizing the surroundings also being desirable for reasons of cost.
EP 1 826 736 B1 discloses a motor vehicle having a device for recognizing road signs, wherein, depending on the probability of the correctness of the sensing of a road sign or its regulatory content, the outputting of a representation of the road sign in a display can vary between a first output form with relatively low probability and a second output form with relatively high probability.
EP 1 131 803 B1 discloses a device and a method for recognizing road signs, image data of an image sensor being analyzed and classified in an information processing unit in order to determine whether the image data of the image sensor contain objects which have a sufficient probability of being road signs. These objects are then fed to a further processing and classification means, wherein separation into road-sign specific upper classes and lower classes is performed. Class-specific feature data are then replaced by corresponding image data that is stored in a memory unit or by image data originating from the image sensor as a function of whether said feature data has been recognized with a high probability during the classification, and the image data resulting from this replacement are combined to form a synthetic image of a road sign which is stored in the memory unit and displayed in the display unit. In this context, the display unit can contain, inter alia, a setting unit by means of which the maximum duration of the display of the synthetic image is set. Furthermore, the display unit can be controlled in such a way that it displays the synthetic image until a predefined distance has been traveled.
DE 296 10 677 U1 discloses an arrangement for displaying road signs, which arrangement has, in addition to a display face for displaying messages to the driver, a signal transmitter which activates the display as a function of the distance traveled, and makes the display visible or deletes it again.
DE 198 29 162 A1 discloses the use of an electronic camera and of an image recognition device cooperating therewith, for the purpose of recognizing road signs, wherein the image recognition device can be reset to its starting state if, the vehicle turns off the road, for example after a road sign indicating a speed limit.